Anyone
who has soldered vertical or steep pitch seams knows how
much harder it is than horizontal seams. You need the solder
to melt so that it can get drawn into the seam, but the
moment it melts, gravity wants it to run down away from
your iron. Here is a method that works well on riveted
lap joints.

1.
Start with an iron with a 3-sided, pointed "knife" shape
(as opposed to the classic pointed, 4-sided shape) slightly
cooler than you would use on a horizontal joint.

2. Starting at the bottom of the joint, with the tip of the iron pointed down, apply a trail of solder at the edge
of the over-lapping metal. Move the iron up the length
of the joint fairly quickly and don't try to heat the
metal, just leave a narrow, vertical trail of solder.
If it doesn't stick to the metal, use more flux until
it does.

3. Go back to the bottom, only this time place the sharp
edge of the blade across the surface of the joint and
again leave a trail of solder. It should be about 1-1 ½ inches
wide, which is determined by the length of the blade
of the iron. This should also go fairly quickly and not
heat the metal much. Again, use flux if needed. The entire
joint should now be covered with a gloppy layer of solder.

4. Repeat the first step of #3, except don't add any more
solder, and this time, move up the joint slowly so that
the metal heats enough to draw the solder in between
the layers, and to seal around the rivets. Only the sharp
edge of the blade should be touching the metal. If done
properly, the solder will pool on top of the blade of
the iron long enough to be drawn into the joint. Some
of the solder will run down the face of the joint, but
it should quickly harden again before reaching the bottom.
If it all runs straight to the bottom, then the metal
is too hot. Repeat this step 3 or 4 times.

5. Once you are confident that the solder has sealed the
joint, start at the top and clean off the excess solder with the sharp edge of the blade. Just smooth it off
with one quick swipe, leaving a layer of solder behind.
There will be a pile of solder below that will have to
be cleaned up. If the vertical joint is part of a gutter,
then you can use this excess to solder the bottom joint.

A
finished vertical seam on a flat-lock copper roof
with built-in gutters (above).